For much of the last year, the University of Wyoming and a company called Audible Magic tested technology that looked inside students' file swaps for copyrighted music, with an eye toward ultimately blocking the transfer of such material.

The job turned out to be harder than Audible Magic expected. On Wednesday, the company said it had given up on part of its network-spying technology and had instead teamed up with an established network-security company. The identify-and-block product still will be offered, but it will now be a joint venture between Audible Magic and security company Palisade Systems, the companies said.

"We recognized that we would have challenges trying to work with the type of bandwidth we were looking for, (such as) inside an ISP," said Audible Magic Chief Executive Vance Ikezoye.

The product is one of the most ambitious among those being designed to rein in unauthorized trades of copyrighted works online, and it carries with it some of the most potentially serious privacy concerns. Most other services, such as Packeteer, work by blocking or controlling the amount of bandwidth available to file-trading applications, rather than by looking inside the transmissions themselves.

Audible Magic's own technology specializes in identifying songs by their digital "fingerprints," or acoustic characteristics.

But combined with Palisade's network-security technology, it could become a powerful monitoring tool for network administrators or copyright holders. The joint product is designed to intercept all traffic on a network, make a copy of it, and then make a running examination of that copy for items such as Kazaa or Gnutella traffic.

When it finds digital packets originating from file-swapping software packages, it will compare the contents against Audible Magic's database of fingerprints. If it finds a match to a copyrighted song, it will stop the transmission of a song in progress, even if some of the file has already been transferred.

"The nice thing about content--if you've only got half of a song, it's worthless," Ikezoye said. "I think in general it's about a third of the way in that we ID and block" an average song.

Analysts say the product is likely to be well received by universities and companies. Internet service providers, which are typically protective of their subscribers' privacy, might be a more difficult sell, however.

"I don't think Comcast or Verizon would voluntarily put this kind of monitoring in place," said Forrester Research analyst Josh Bernoff. "Users would consider it intrusive."